Despite significant advances in the treatment of diabetes mellitus over the past several years, diabetes remains the major cause of renal failure in the Western world today. While most scientists agree that kidney failure in diabetes results from the abnormal diabetic environment, the mechanisms by which a chronic increase in blood glucose causes kidney failure are still an enigma. Recent studies have demonstrated the importance of mesangial expansion in the development of the clinical features of diabetic nephropathy. It is hypothesized that expansion of the glomerular mesangium by normal matrix constituents eases narrowing and obliteration of the glomerular capillary lumen, thereby decreasing the filtering surface of the glomerulus. The overall goal of this project is to elucidate the mechanisms for mesangial matrix expansion in the diabetic kidney. This will be accomplished primarily by studying the effects of advanced products of tissue glycosylation on the development of diabetic kidney disease, and specifically on the mesangial cell. The several approaches taken in this work are designed to address both the direct involvement of mesangial cells in this process and the role played by individual cytokines produced by mesangial and other cells. The specific objectives of the current proposal are: 1) to assess the direct effects of advanced glycosylation end products (AGEs) on mesangial cells, by determining the effects of AGEs on both MC proliferation and on expression of the genes for cytokines (interleukin-l (IL-l), cachectin/tumor necrosis factor (TNF), and platelet-derived growth factor) and for matrix glycoproteins (collagen type IV and fibronectin); 2) to determine whether mesangial cells, like macrophages, contain a specific receptor for AGE-modified proteins; 3) to determine whether AGE-stimulated macrophages can have a paracrine effect on MCs in vitro; 4) to determine whether whole kidneys, glomeruli, and blood-derived kidney macrophages obtained form diabetic animals express increased levels of MRNA for IL-l and TNF when compared to those obtained from control animals; 5) to determine whether animals depleted of blood-derived kidney macrophages are protected from the development of diabetic kidney disease; 6) to assess the effects of matrix glycoproteins (collagen type IV and fibronectin) on MCs, and to study whether these affects can be altered by glycosylation of the matrix proteins. These studies should lend insight into important molecular events leading to the development of diabetic kidney disease, and should clarify the role played by advanced glycosylation end products in this process. These findings would provide the rationale for designing therapies directed at preventing this chain of events.